It is the goal of this study to determine the metabolism and kinetic disposition of opiates (morphine) and their antagonists in experimental animals and to correlate pharmacokinetic data with in vivo stereospecific cerebral binding and pharmacological effects. The nature and function of high affinity cerebral binding will be studied in vivo using labeled tracer doses of opiate agonists and antagonist in the presence of pharmacological amounts of unlabeled drugs. These studies are designed to determine which drug-receptor binding interactions are responsible for analgesia, dependence and tolerance. The hypothesis will be tested, whether the rate of morphine removal from cerebral binding sites correlates to withdrawal after an episode of morphine addiction.